1. Field of the Invention
The present invention relates to a process and an apparatus for manufacturing tyres for vehicle wheels.
2. Description of the Related Art
A tyre generally comprises a carcass structure comprising at least one carcass ply formed of reinforcement cords incorporated in an elastomeric matrix. The carcass ply has end edges respectively engaged with annular anchoring structures. The latter are arranged in the areas of the tyre usually identified by the name “beads” and they are normally formed each by a substantially circumferential annular insert on which at least one filling insert is applied, in a radially outer position thereof. Such annular inserts are commonly identified as “bead cores” and have the task of keeping the tyre firmly fixed to the anchoring seat specifically provided in the rim of the wheel, thus preventing, in operation, the radially inner end edge of the tyre coming out from such a seat.
At the beads specific reinforcement structures may be provided having the function of improving the torque transmission to the tyre.
The carcass structure is formed on a forming support preferably having a substantially cylindrical shape.
In a radially inner position with respect to the carcass ply(plies) a coating layer made from elastomeric material, typically known as “liner”, is typically provided.
In a radially outer position with respect to the carcass structure, on the other hand, a belt structure is associated.
The belt structure is generally made on a different forming support from the one on which the carcass structure is formed.
The belt structure comprises one or more belt layers arranged radially one on top on the other and having textile or metallic reinforcement cords arranged preferably according to an inclined orientation with respect to the circumferential direction of the tyre and normally crossed with respect to the cords of the possible adjacent belt layer.
The belt structure can also comprise at least one reinforcing structure defined by at least one continuous elongated reinforcing element including at least one textile or metallic reinforcement cord incorporated in a matrix of elastomeric material and extending parallel to the longitudinal direction of the elongated element itself.
The continuous elongated reinforcing element is wound on the forming support—typically on a radially outer surface of at least one belt layer deposited on the forming support—according to axially adjacent circumferential coils to form the so-called “zero degree layer”. Such a term is used to define a layer wherein the reinforcing cords have an orientation substantially coinciding with a circumferential direction of the tyre.
According to the needs, and in particular in tyres for heavy vehicles, one or more zero degree layers can be provided, each of which extending along the entire width of the belt structure or along a portion of the axial extension thereof (in this last case, normally, at the axially outer end portions of the underlying belt layer).
Between the carcass structure and the belt structure a layer of elastomeric material, known as “under-belt”, can be provided, said layer having the function of making the radially outer surface of the carcass structure as uniform as possible for the subsequent application of the belt structure.
In a radially outer position with respect to the belt structure a tread band is applied, also made from elastomeric material, as well as other structural elements making up the tyre.
On the side surfaces of the carcass structure respective sidewalls of elastomeric material are also applied, each extending from one of the side edges of the tread band up to the respective annular anchoring structure to the beads.
Throughout the present description and in the subsequent claims, the terms “radial” and “axial” and the expressions “radially inner/outer” and “axially inner/outer” are used with reference to the radial direction and to the axial (or longitudinal) direction of a tyre (or of the forming support used to manufacture a specific component of the tyre). The terms “circumferential” and “circumferentially”, on the other hand, are used with reference to the annular extension of the tyre/forming support.
Throughout the present description, unless specified otherwise, and in the subsequent claims, “continuous elongated reinforcing element” is used to indicate an element comprising at least one steel reinforcing cord incorporated in a matrix of elastomeric material and extending parallel to a longitudinal direction of said continuous elongated reinforcing element.
Throughout the present description and in the subsequent claims, the definitions “upstream” and “downstream”, unless indicated otherwise, refer to the feeding direction of the continuous elongated reinforcing element towards a forming support.
Moreover, when throughout the present description and in the subsequent claims reference is made to the feeding direction of the continuous elongated reinforcing element, it is specifically referred, unless indicated otherwise, to a theoretical line at the lower surface of the continuous elongated reinforcing element during its movement towards the forming support.
WO 2007/054984 to the same Applicant describes an apparatus and a process for the manufacturing of zero degree reinforcement structures by deposition, on a substantially cylindrical forming support, of a continuous elongated reinforcing element comprising textile or metallic cords. The apparatus comprises a base with which an arm is associated that can oscillate, when driven by a suitable fluid-dynamic actuator, between a rest position in which the arm is in a distal position from the forming support and an operative position in which the arm is in a proximal position to the forming support so as to allow the deposition of the aforementioned continuous elongated reinforcing element.
Such a continuous elongated reinforcing element is unwound from a collection reel and, through suitable deviating pulleys, fed through the aforementioned arm towards the forming support. Such an arm comprises, in particular, a deviating pulley in an inlet portion thereof and an end block in an outlet portion thereof. The end block acts as a guide channel of said continuous elongated reinforcing element towards the forming support.
At least one pressing roller is hinged to the end block; when a second fluid-dynamic actuator is actuated, at least one pressing roller can be moved between a rest position in which it is away from the forming support and a work position in which it operates in thrusting relationship on said continuous elongated reinforcing element so as to deposit it onto the forming support.
The oscillating arm also carries at least one shearing unit which can be selectively activated at the end of the deposition step described above to cut said continuous elongated reinforcing element in a portion located between the end block and the inlet pulley, and an advancing device for bringing the top free end of said continuous elongated reinforcing element in a canti-levered position with respect to the end block and at the pressing roller, so as to be able to start with a new deposition cycle.